I went to the apiary this morning for Miriam's weekly inspection. As usual, everything in her hive is fine, the bees are well-behaved and there were a few empty queen cups but no signs of swarm planning. She is such an easy-going queen...!
Then, I decided to have a sneak peak in the nucleus. The bees were noticeably calmer than on Friday - which I took to be a positive sign. Then, when I was inspecting the second frame I heard a distinctive sound, pitched between G natural (783.99 Hz) and G# (830.61 Hz) - a long note lasting around a second, followed by two shorter ones. It sounds almost like a "D" in Morse Code, but slowed down. I knew immediately what this was - a new queen, piping!
Queen piping is a phenomenon only heard when there is a newly emerged queen, usually less than a week old. There are a few opinions about why new queens do this, but the one that seems most likely is it is part of the process of establishing that the hive has a queen. Worker bees are normally aware of the presence of a queen from the pheromones she produces. However, newly-emerged queens produce less pheremone. So, the piping seems to be a way of announcing herself to the rest of the hive, to cover the period until she is producing enough pheremone. She is, literally, playing her own royal fanfare! If we were to anthropomorphise this any further, we might expect her to be a little disappointed that she has to play the fanfare herself. But that's bees for you...
The mechanism by which she does this is interesting - and I was lucky enough to watch it for myself today. The queen will stop at a certain point on the wax comb, grip with her feet and press the underside of her thorax onto the comb. She then vibrates her thorax (using her wing muscles, I assume) and the vibrations reverberate through the comb. Any worker bees on the same comb will be in no doubt that a queen is present, as they will feel the vibrations. I wonder if this also has a secondary function of strengthening the queen's wing muscles, as she will shortly have to leave the hive to go on mating flights.
So - a new queen in the nucleus - what good news!
I decided to push my luck a little further, and see what was happening in the queenless hive. The bees were still in a decidedly truculent mood, so I was pessimistic. I got to the frame with the queen cell on it, and could see the end nicely chewed until it was paper-thin. But, it was still sealed. At this point, I decided to do something I have read about, but never before tried myself. I played midwife! Carefully, with the sharp corner of my hive tool, I picked at the end of the queen cell until there was a small tear in the wax. I was delighted to see movement - the head of the queen bee inside the cell. After I'd held the frame for a minute more, she finished nibbling open the end and marched straight out of the cell. New queens move really fast - the movement is actually quite distinctive, which makes them fairly easy to spot. No piping this time, as she was walking over the backs of the worker bees. I decided to close up the hive straight away, and let her get on with the important job of getting to know her new kingdom.
So, what a difference from the frustration of Friday - two new queen bees! Yes, I am feeling very proud!
Sunday 28 May 2017
Saturday 27 May 2017
One Queen, Two Queen, Hatched Queen, Flew Queen
So, if you read last week's Update on the Queens, you'll know that I was expecting a queen to emerge from the queen cell that the bees have been carefully growing and nurturing. So yesterday I opened up the hive to see if she has indeed emerged. Regular reader Stewart was on-hand to take photos, and when we lifted the frame with the queen cell, we saw this:
You can see that the end of the cell has been carefully cut through, and at the bottom end a flap of wax has hinged open. The queen is out! But where is she?
There was only one way to find out - I needed to go through every frame, and try to find the queen. The first thing I noticed is the bees were still in a bad mood. This was surprising, as they usually calm down when the new queen emerges. Then, 4 frames in, I found two "emergency" queen cells, still unopened. I thought I'd checked through very carefully last week, but clearly I hadn't checked well enough. And, given the colony size (very big!) and the weather (warm and sunny), I started to suspect that the queen may have emerged and then swarmed. Bees will do this if the colony is big and there are other queen cells in reserve. I had to be sure, so I kept going. More queen cells on frame 5, and still no sign of the queen. I pressed on, and didn't see her anywhere in the brood box.
Back to the super box, and I went through frame-by-frame - still no sign of the queen. Then, on the 8th frame, I found this:
Another primary queen cell! I'd made the mistake of not looking through the super frames last week (I'd taken several stings by that point, and decided to give up), and therefore never seen this queen cell before. So, what to do?
Firstly, I had to decide whether I had a queen or not. There were two possibilities:
So, that's the plan. Will it work? Difficult to say - so far the bees haven't thought much of my plans, they seem to prefer their own!
You can see that the end of the cell has been carefully cut through, and at the bottom end a flap of wax has hinged open. The queen is out! But where is she?
There was only one way to find out - I needed to go through every frame, and try to find the queen. The first thing I noticed is the bees were still in a bad mood. This was surprising, as they usually calm down when the new queen emerges. Then, 4 frames in, I found two "emergency" queen cells, still unopened. I thought I'd checked through very carefully last week, but clearly I hadn't checked well enough. And, given the colony size (very big!) and the weather (warm and sunny), I started to suspect that the queen may have emerged and then swarmed. Bees will do this if the colony is big and there are other queen cells in reserve. I had to be sure, so I kept going. More queen cells on frame 5, and still no sign of the queen. I pressed on, and didn't see her anywhere in the brood box.
Back to the super box, and I went through frame-by-frame - still no sign of the queen. Then, on the 8th frame, I found this:
Another primary queen cell! I'd made the mistake of not looking through the super frames last week (I'd taken several stings by that point, and decided to give up), and therefore never seen this queen cell before. So, what to do?
Firstly, I had to decide whether I had a queen or not. There were two possibilities:
- I have a queen, but she is out mating
- I had a queen, but she has swarmed
Scenario [1] was possible, but I would have expected the bees to be in a better mood if the queen had stayed. So, I decided I had to accept that she had probably swarmed. What to do next?
There is a risk that each queen in each of the remaining queen cells will also swarm, until they are down to the last queen cell. I need to minimise the chances of that happening. So I decided to split the colony, and spread the risk.
I took out frames 1-5 from the brood box, where I'd seen the emergency cells, and put them (with plenty of bees) into a nucleus box. I then put 5 new, empty frames into hive and closed up. Here's what I now have:
- The hive contains (probably) one primary queen cell (on super frame #8). I'm expecting the queen to emerge in the next couple of days, and hopefully not swarm. She will then take over the hive.
- The nucleus contains 3 or 4 queen cells. I'm hoping the bees will recognise that their colony is too small to swarm, and that when the first queen emerges she will kill her sisters and take over the colony.
So, that's the plan. Will it work? Difficult to say - so far the bees haven't thought much of my plans, they seem to prefer their own!
Tuesday 23 May 2017
Update on the Queens
Here's a quick update on what's going on with the queens in my hives:
Miriam's bees were very well behaved when I opened up their hive on Sunday. There were a few "queen cups", but none of them had eggs in them. From this, I conclude that they are not planning to swarm at the moment, probably because it rained on most days last week. Now that the sun is out, I will need to keep a closer eye on them in case they change their minds!
I took Caroline out and moved her into the nucleus box two weeks ago. You may remember that this was because I found a queen cup with an egg in it. This has now been grown into a lovely big queen cell, with the new queen pupating inside. This is very good news!
However, the bees have developed an "insurance policy". As well as the queen cell that they planned, they had also created four "emergency" queen cells, as backup in case there's a problem with the one they planned. So, basically, the hive had an heir, and four spares.
This is good for the bees, but not so good for me. A beehive normally only has one queen, and this situation could lead to (up to) five queens emerging from their cells this week. The problem comes down to this: if I were to leave more than one queen cell in the hive, the queens will either fight or swarm when they emerge from the cells - and I don't want either to happen.
So, the main job of Sunday afternoon was to go through and remove the other queen cells, leaving just the big one. This should have been a straightforward job - apart from needing sharp eyes to spot the additional cells, there really isn't much to it. Unfortunately, the bees were very defensive on Sunday (no doubt defending their precious queen cells) so I got several stings for my trouble. Still, I got it done in the end.
Fellow Widcombe resident Stewart was on hand to take some photos, and got this great picture of the queen cell:
If you look closely (you'll probably have to view the photo full-screen), you'll notice that the (bottom) end looks a little ragged and there is a darker band around the cell near the bottom tip. This is because the queen is nearly ready to emerge (around 1-2 days from emerging) so the worker bees are chewing away the cell tip to make the wax layer thinner, so that it will be easier for the queen to bite through the wax and emerge. You can actually see the worker bees nibbling away in the photo!
Based on when I first saw the egg, and the condition of the queen cell in the photo, I would estimate that the cell is 14 days old. Queen bees emerge 16 days after being laid, and the photo was taken two days ago, so hopefully I should have a new queen bee today!
This next photo is interesting - one of the queen cells got sheared off as I was removing a box of frames for the inspection. This cell was probably 10-11 days old, i.e. recently capped and still had royal jelly inside (the queen larva hadn't yet eaten it all). In this picture you're looking from the bottom of the cell (sheared off around half-way) up to the top. The queen larva has been removed, and you can see the layer of royal jelly. The worker bees are taking an interest because they are going to eat the royal jelly, prior to dismantling the cell:
The next inspection will be on Saturday - hopefully I will get my first look at the new queen!
Miriam's Hive
Miriam's bees were very well behaved when I opened up their hive on Sunday. There were a few "queen cups", but none of them had eggs in them. From this, I conclude that they are not planning to swarm at the moment, probably because it rained on most days last week. Now that the sun is out, I will need to keep a closer eye on them in case they change their minds!
The Queenless Hive (Formerly Caroline's Hive)
I took Caroline out and moved her into the nucleus box two weeks ago. You may remember that this was because I found a queen cup with an egg in it. This has now been grown into a lovely big queen cell, with the new queen pupating inside. This is very good news!
However, the bees have developed an "insurance policy". As well as the queen cell that they planned, they had also created four "emergency" queen cells, as backup in case there's a problem with the one they planned. So, basically, the hive had an heir, and four spares.
This is good for the bees, but not so good for me. A beehive normally only has one queen, and this situation could lead to (up to) five queens emerging from their cells this week. The problem comes down to this: if I were to leave more than one queen cell in the hive, the queens will either fight or swarm when they emerge from the cells - and I don't want either to happen.
So, the main job of Sunday afternoon was to go through and remove the other queen cells, leaving just the big one. This should have been a straightforward job - apart from needing sharp eyes to spot the additional cells, there really isn't much to it. Unfortunately, the bees were very defensive on Sunday (no doubt defending their precious queen cells) so I got several stings for my trouble. Still, I got it done in the end.
Fellow Widcombe resident Stewart was on hand to take some photos, and got this great picture of the queen cell:
If you look closely (you'll probably have to view the photo full-screen), you'll notice that the (bottom) end looks a little ragged and there is a darker band around the cell near the bottom tip. This is because the queen is nearly ready to emerge (around 1-2 days from emerging) so the worker bees are chewing away the cell tip to make the wax layer thinner, so that it will be easier for the queen to bite through the wax and emerge. You can actually see the worker bees nibbling away in the photo!
Based on when I first saw the egg, and the condition of the queen cell in the photo, I would estimate that the cell is 14 days old. Queen bees emerge 16 days after being laid, and the photo was taken two days ago, so hopefully I should have a new queen bee today!
This next photo is interesting - one of the queen cells got sheared off as I was removing a box of frames for the inspection. This cell was probably 10-11 days old, i.e. recently capped and still had royal jelly inside (the queen larva hadn't yet eaten it all). In this picture you're looking from the bottom of the cell (sheared off around half-way) up to the top. The queen larva has been removed, and you can see the layer of royal jelly. The worker bees are taking an interest because they are going to eat the royal jelly, prior to dismantling the cell:
The next inspection will be on Saturday - hopefully I will get my first look at the new queen!
Monday 15 May 2017
Caroline's New Home
I mentioned in last week's post that our local councillor, Ian, has been helping me at the apiary so that he can improve his beekeeping skills. Well, after Caroline was moved into the nucleus last week, she was looking for a new owner. And Ian has been wanting to get some bees of his own. So, after a little bit of match-making on my part, Ian is now the owner of Caroline and her bees!
We met at dusk on Friday for Ian to make the pickup. Which sounds dramatic (maybe?) but really is just practicality - moving a nucleus during daylight hours is not a good idea, because all the foraging bees will still be outside collecting nectar and pollen. Bees stop flying when the sun sets, so dusk is the perfect time to move a nuc (or hive) to make sure that all the bees are at home.
There isn't a lot to moving a nuc or hive, actually - you need to put a ratchet strap round under the floor and over the roof to hold everything together. And the entrance block has to be rotated to the "closed" position, and held in place with gaffer tape. Once that's done, everything is bee-proof and ready to go.
We took the nuc to Ian's garden, and placed it on the spot where his hive will be. I removed the gaffer tape, but left the entrance block closed, and then left Ian to wait for an hour while the bees settled down from their journey. Ian then turned the entrance block to the "open" position, so that in the morning the bees would be able to get out and about.
We left the bees alone on Saturday, and then I went back to Ian's garden on Sunday to help move the bees into the new hive that Ian has built. We moved the bees frame-by-frame, did a quick check to see if Caroline was still present (yes) and laying (yes), and then put the roof on. Job done, and here's Caroline's new home in Ian's garden:
A brief update on my hives: Miriam's bees are doing well, and I added another box of honey frames to the hive on Saturday. I found one queen cup with an egg in it, and cut it off the comb. I will need to let the colony re-queen (i.e. replace Miriam) at some point this year, but ideally I'd prefer to wait until I have a laying queen in the other hive.
Looking into the queenless hive (formerly the Kingdom of Caroline), I located the queen cup which had an egg in it last week. The bees have done a great job and grown a lovely big queen cell - one of the best I've seen! There was another one on the adjacent frame, and no doubt there are more in the brood box, but I decided not to disturb the bees too much this week. Next week I will need to go through and remove the other queen cells, leaving just the big one.
We met at dusk on Friday for Ian to make the pickup. Which sounds dramatic (maybe?) but really is just practicality - moving a nucleus during daylight hours is not a good idea, because all the foraging bees will still be outside collecting nectar and pollen. Bees stop flying when the sun sets, so dusk is the perfect time to move a nuc (or hive) to make sure that all the bees are at home.
There isn't a lot to moving a nuc or hive, actually - you need to put a ratchet strap round under the floor and over the roof to hold everything together. And the entrance block has to be rotated to the "closed" position, and held in place with gaffer tape. Once that's done, everything is bee-proof and ready to go.
We took the nuc to Ian's garden, and placed it on the spot where his hive will be. I removed the gaffer tape, but left the entrance block closed, and then left Ian to wait for an hour while the bees settled down from their journey. Ian then turned the entrance block to the "open" position, so that in the morning the bees would be able to get out and about.
We left the bees alone on Saturday, and then I went back to Ian's garden on Sunday to help move the bees into the new hive that Ian has built. We moved the bees frame-by-frame, did a quick check to see if Caroline was still present (yes) and laying (yes), and then put the roof on. Job done, and here's Caroline's new home in Ian's garden:
A brief update on my hives: Miriam's bees are doing well, and I added another box of honey frames to the hive on Saturday. I found one queen cup with an egg in it, and cut it off the comb. I will need to let the colony re-queen (i.e. replace Miriam) at some point this year, but ideally I'd prefer to wait until I have a laying queen in the other hive.
Looking into the queenless hive (formerly the Kingdom of Caroline), I located the queen cup which had an egg in it last week. The bees have done a great job and grown a lovely big queen cell - one of the best I've seen! There was another one on the adjacent frame, and no doubt there are more in the brood box, but I decided not to disturb the bees too much this week. Next week I will need to go through and remove the other queen cells, leaving just the big one.
Monday 8 May 2017
In The Apiary This Weekend
After a cold spell that meant I couldn't open up the hives for a fortnight, we finally got some warmer weather yesterday. So - what's been happening?
Starting with Miriam's colony, everything looks fine. She is laying, there are plenty of bees and there is nectar coming in. There are two boxes (supers) of honey frames on the hive, and the first one (the one they will use as winter stores) is already full. The second super is mostly empty at the moment, but there are a couple of frames where the bees have started storing nectar.
Local councillor Ian was helping me with the inspection yesterday, and we were mainly focused on looking for queen cells, as these are a sign the colony is planning to swarm. We had a good look in Miriam's hive but couldn't see any, so hopefully her colony will stay nice and calm for the next few weeks.
On to Caroline's hive. This is the one where the queen has been allowed to lay in both the brood-box and the first (bottom) super - an arrangement known as "brood-and-a-half". It means she has around 60% more laying space than Miriam, which means lots more bees! The difference is noticeable - Ian and I were greeted with a very busy colony when we opened up. Unfortunately, there was no time for photos as we had our hands full just checking everything in the hive.
Looking through the brood frames, there were a few empty queen "cups" - these are concave wax structures that face downwards, and are the foundation for a queen cell. One possibly had an egg in it, but I squished it while I was opening up the cell with my hive tool to get a closer look.
On to the brood-containing super. The first frame was mostly honey, then two frames full of worker brood. And then on frame number four, I saw what we were looking for - a queen cup with an egg clearly laid inside it. This means the colony is starting to make swarm preparations, with the likely swarm date in around 8-9 days time. I don't want my bees to swarm, so I had two options - either remove the egg, to delay their plans, or remove the queen. I decided that removing the egg would only delay the inevitable, and I'd rather solve the issue as early as possible in the season. But what do I do with the queen?
Well, the first thing I needed to do was find her! Ian and I went back through the brood box for a second time, trying to find the queen. Believe me, when you are looking through thousands of bees, trying to find one that looks slightly different, this is no easy task. She made us work for it, too - there are 11 frames in the brood box, and we didn't find her until frame number 9.
So, having now found her, we needed to take her out of the hive and give her a new place to live. Beekeepers have a piece of equipment for this - a half-width brood box called a "nucleus" (often abbreviated to "nuc"). I have two empty nucleus boxes at the moment, so we brought one down next to the hive, and transferred the frame bearing the queen into it. A nuc takes 5 frames in total, so I added another frame of bees and brood, plus a frame of bees and honey (they'll need something to eat while they're getting settled into their new home). I had two partially-drawn (but empty) brood frames that I'd stored over the winter, so I put those in as well - these will give queen Caroline extra space to lay in. And then put the roof on, and the nucleus was complete.
The now-queenless hive needed three new frames to replace the three I'd just transferred to the nuc. I found three new frames from my spares box, put them in and then Ian and I re-assembled the hive. Then there was one last job: the colony had filled both their supers, so we needed to add another one. I had a spare one ready to go, and added it to the hive, which will give the bees something to work with while they wait for the new queen egg to hatch and grow.
I've been very pleased with the rate of honey collection this year - the bees have started earlier, and collected faster than last year. There is a great variety of forage around at the moment, including trees and garden flowers. Here's a picture I took of one of my bees foraging last week on some bluebells round the corner from the hives:
It's always great to see the horse chestnut in flower - the flowers are great forage for bees, and they bring lots of the brick-red pollen into the hive. Here's a picture taken near Bath Spa railway station, showing the wonderful "candles" of flowers:
Starting with Miriam's colony, everything looks fine. She is laying, there are plenty of bees and there is nectar coming in. There are two boxes (supers) of honey frames on the hive, and the first one (the one they will use as winter stores) is already full. The second super is mostly empty at the moment, but there are a couple of frames where the bees have started storing nectar.
Local councillor Ian was helping me with the inspection yesterday, and we were mainly focused on looking for queen cells, as these are a sign the colony is planning to swarm. We had a good look in Miriam's hive but couldn't see any, so hopefully her colony will stay nice and calm for the next few weeks.
On to Caroline's hive. This is the one where the queen has been allowed to lay in both the brood-box and the first (bottom) super - an arrangement known as "brood-and-a-half". It means she has around 60% more laying space than Miriam, which means lots more bees! The difference is noticeable - Ian and I were greeted with a very busy colony when we opened up. Unfortunately, there was no time for photos as we had our hands full just checking everything in the hive.
Looking through the brood frames, there were a few empty queen "cups" - these are concave wax structures that face downwards, and are the foundation for a queen cell. One possibly had an egg in it, but I squished it while I was opening up the cell with my hive tool to get a closer look.
On to the brood-containing super. The first frame was mostly honey, then two frames full of worker brood. And then on frame number four, I saw what we were looking for - a queen cup with an egg clearly laid inside it. This means the colony is starting to make swarm preparations, with the likely swarm date in around 8-9 days time. I don't want my bees to swarm, so I had two options - either remove the egg, to delay their plans, or remove the queen. I decided that removing the egg would only delay the inevitable, and I'd rather solve the issue as early as possible in the season. But what do I do with the queen?
Well, the first thing I needed to do was find her! Ian and I went back through the brood box for a second time, trying to find the queen. Believe me, when you are looking through thousands of bees, trying to find one that looks slightly different, this is no easy task. She made us work for it, too - there are 11 frames in the brood box, and we didn't find her until frame number 9.
So, having now found her, we needed to take her out of the hive and give her a new place to live. Beekeepers have a piece of equipment for this - a half-width brood box called a "nucleus" (often abbreviated to "nuc"). I have two empty nucleus boxes at the moment, so we brought one down next to the hive, and transferred the frame bearing the queen into it. A nuc takes 5 frames in total, so I added another frame of bees and brood, plus a frame of bees and honey (they'll need something to eat while they're getting settled into their new home). I had two partially-drawn (but empty) brood frames that I'd stored over the winter, so I put those in as well - these will give queen Caroline extra space to lay in. And then put the roof on, and the nucleus was complete.
The now-queenless hive needed three new frames to replace the three I'd just transferred to the nuc. I found three new frames from my spares box, put them in and then Ian and I re-assembled the hive. Then there was one last job: the colony had filled both their supers, so we needed to add another one. I had a spare one ready to go, and added it to the hive, which will give the bees something to work with while they wait for the new queen egg to hatch and grow.
I've been very pleased with the rate of honey collection this year - the bees have started earlier, and collected faster than last year. There is a great variety of forage around at the moment, including trees and garden flowers. Here's a picture I took of one of my bees foraging last week on some bluebells round the corner from the hives:
It's always great to see the horse chestnut in flower - the flowers are great forage for bees, and they bring lots of the brick-red pollen into the hive. Here's a picture taken near Bath Spa railway station, showing the wonderful "candles" of flowers:
Tuesday 2 May 2017
A - C - G - T: I Can Make A Honey Bee!
Science warning: this post contains actual science. You have been warned...
A few weeks ago, I wrote a blog post about drones. And, despite the cheeky science warning (repeated here!), regular reader Sophie asked this:
Thirdly, yes - Xo does indeed present as male in bees. But, it isn't quite as straightforward as saying that "XX is female and Xo is male", even though that is what appears to be going on.
So, if it isn't straightforward, then what is actually going on? Time to delve right down into the cellular nucleus, and explore the strange world of honey bee genetics...
Firstly, a reminder about the basics in humans. All our genes are encoded in sequences of DNA. And the DNA (which is basically a very long molecule) is bundled up in separate packages called chromosomes. When we started off as a single fertilised egg (which is just one cell), that egg contained 46 chromosomes (occasionally, someone will have 47, which leads to conditions such as Down syndrome and Klinefelter syndrome). As we grow, cells get copied over and over again, and each new cell gets its own copy of the 46 chromosomes.
23 of the chromosomes came from our mother (from the unfertilised egg) and the other 23 from our father (from the sperm). And they're not just random - each maternal chromosome has an equivalent paternal chromosome, so they form pairs. The chromosomes in each pair are similar but not the same - that is to say, if you take a maternal/paternal pair, they will control the same set of genes, but may have different versions of each gene. So, if we look at chromosome pair 15, we find the gene for eye colour. The maternal version might be the gene for brown eyes, whereas the paternal version might be the gene for blue eyes.
These two different versions of the same gene are called alleles. And we'll come back to them later on...
One pair of chromosomes in humans is different - pair 23 is the sex chromosomes. The one inherited from the mother looks just the same as the other chromosomes, and is referred to as the "X" chromosome. The one inherited from the father comes in two versions. Version 1 is also an "X" chromosome (and the father inherited it from his mother). Version 2 is much smaller, a stubby little chromosome that contains far fewer genes. This is the "Y" chromosome. And the simple rule is that if you get two X chromosomes (i.e. you are XX) then you are female, whereas if you get an X and a Y (you are XY) then you are male. interestingly, pair 23 is the one pair of chromosomes where a gene on one (the X) may not have a match on the other (if it's Y). For example, the gene that determines colour-blindness is carried only on the X chromosome.
But we digress - this is supposed to be about bees!
There are two big differences in honey bees. Firstly, there are only 16 pairs of chromosomes. And secondly, only female bees get their chromosomes in pairs (i.e. a set from both parents for a total of 32). Male bees only have 16 unpaired chromosomes - all from their mother. Bee eggs are completely capable of developing into adult bees even if they are unfertilised - and they will always be male in this case. This process of being able to create children without fertilisation is known as parthenogenesis. And (male) bees produced through parthenogenesis have half as many chromosomes, so they are referred to as being "haploid". Female bees, with the full complement of 32 chromosomes, are "diploid".
Now, one of the consequences of this is that there is no Y chromosome. It's still the case that female bees are XX, but male bees only have one (of each) X chromosome - this is denoted as "Xo" (the "o" denoting "missing" or "absent").
So, one X makes a bee male, two XX makes her female, right? Well, this is what was thought until 2003, when researchers from the University of California found out it doesn't quite work like that. They found that sex determination isn't actually done by chromosome count - there's a specific gene that controls it. The gene is on the 3rd chromosome, and is called the "csd" or "complementary sex-determination" gene. Now, you might assume that this gene comes in two versions - male and female. But that would mean that a haploid (Xo) bee could have the "female" version in its one copy of chromosome 3 - in other words, a bee from an unfertilised egg could become female. But that never happens. So, what's actually going on?
It comes back to the alleles that we mentioned earlier. Remember the genes for eye colour in humans? These come in a number of different versions (blue, brown, green and others). Each different version of the gene is known as a different allele. And genes with multiple alleles are referred to as polymorphic - meaning that they come in different forms (poly=multiple, morphic=forms).
Now, the clue to how this works is in the name of the gene - "complementary sex-determination" gene. Why complementary? Simply, that different alleles of csd complement each other - in other words, they work together. When a bee has two different - complementary - versions of csd, she becomes female. If a bee has only one version of csd, then he will be male.
So, a quick recap - if a bee is Xo, it can only have one version of csd, so he must be male, and that's exactly what we observe. And if a bee is XX, and the two versions of csd are different (this is known as being heterozygous), then we get a female. There are around 20-25 different alleles of csd, so most of the time this is what happens.
But - hang on - it must be possible, even though unlikely, that sometimes an XX (diploid) bee, will have two identical copies of the csd gene? Indeed it is - in this case the gene is homozygous. But what happens then? Well, csd has a secondary effect - when two identical alleles are present, it changes the relative amounts of certain compounds in the skin of the larva when it hatches. This makes the larva smell different from the others, for around the first three days of its life. In fact, from a worker bee's perspective, it makes the larva smell delicious. So she eats it.
This means that adult bees with two identical csd alleles are never present in the hive. But if a csd-homozygous larva continues to be fed (and isn't eaten!) then it's possible for it to grow into an adult bee. But what does it become? Some scientists wanted to find out, so they hatched some csd-homozygous larvae in a laboratory, and fed them. After three days (when they stopped smelling like a tasty treat) they were returned to the hive where the workers continued to feed them. And then their cells were capped with wax (by the workers, as normal), the larvae underwent metamorphosis and later emerged as adult bees... which turned out to be...
Male! In other words, they are diploid (XX like female workers) but are actually drones. Having one version (but two copies) of the csd gene has the same effect as having only one copy - i.e. the bee is a male drone. But there are subtle differences. They are larger, heavier and have smaller testes. That last point is important - it means that the drones are, effectively, sterile. It is theoretically possible to inseminate a queen with diploid (XX) drone sperm to produced triploid (XXX - wowzers!) bees. But in practice it hasn't been achieved due the the extremely low sperm count of the diploid drones.
So there you have it - a haploid (Xo) bee will be a normal drone. A diploid (XX), csd-heterozygous bee will be a worker. And a diploid (XX), csd-homozygous bee will theoretically grow up to be a fat, sterile drone (but will actually be eaten by his sisters just after he hatches).
I'll leave you with one final fun fact. We've said that there are around 20-25 different alleles of the csd gene. Interestingly, a queen bee will mate with roughly 20-25 males before she starts laying. Co-incidence? I suspect not - it seems that bee mating behaviour has evolved to try to maximise the number of different csd genes, and therefore minimise or eliminate the production of diploid drones in the hive. Isn't that rather clever?
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| The Lego bricks of life! (Wikimedia Commons, Public Domain) |
A few weeks ago, I wrote a blog post about drones. And, despite the cheeky science warning (repeated here!), regular reader Sophie asked this:
"If a male drone is from an unfertilised egg, I assume he is always haploid. However, he must be XY to be male, so where does the extra sex chromosome come from? The egg would presumably always be X, as the queen must be XX. It makes sense that the male would just be Xo because then all the sperm would be X, which accounts for all fertilised eggs developing into females. Can the male spontaneously develop a Y chromosome somehow? Or does Xo present as male in bees?"It's a great question. My initial answers were: Firstly - yes, drones are haploid. Secondly, the sex determination mechanism in bees (and other hymenoptera) isn't done by a dedicated sex chromosome in the way that it is with mammals - so there is no Y chromosome.
Thirdly, yes - Xo does indeed present as male in bees. But, it isn't quite as straightforward as saying that "XX is female and Xo is male", even though that is what appears to be going on.
So, if it isn't straightforward, then what is actually going on? Time to delve right down into the cellular nucleus, and explore the strange world of honey bee genetics...
Firstly, a reminder about the basics in humans. All our genes are encoded in sequences of DNA. And the DNA (which is basically a very long molecule) is bundled up in separate packages called chromosomes. When we started off as a single fertilised egg (which is just one cell), that egg contained 46 chromosomes (occasionally, someone will have 47, which leads to conditions such as Down syndrome and Klinefelter syndrome). As we grow, cells get copied over and over again, and each new cell gets its own copy of the 46 chromosomes.
23 of the chromosomes came from our mother (from the unfertilised egg) and the other 23 from our father (from the sperm). And they're not just random - each maternal chromosome has an equivalent paternal chromosome, so they form pairs. The chromosomes in each pair are similar but not the same - that is to say, if you take a maternal/paternal pair, they will control the same set of genes, but may have different versions of each gene. So, if we look at chromosome pair 15, we find the gene for eye colour. The maternal version might be the gene for brown eyes, whereas the paternal version might be the gene for blue eyes.
These two different versions of the same gene are called alleles. And we'll come back to them later on...
One pair of chromosomes in humans is different - pair 23 is the sex chromosomes. The one inherited from the mother looks just the same as the other chromosomes, and is referred to as the "X" chromosome. The one inherited from the father comes in two versions. Version 1 is also an "X" chromosome (and the father inherited it from his mother). Version 2 is much smaller, a stubby little chromosome that contains far fewer genes. This is the "Y" chromosome. And the simple rule is that if you get two X chromosomes (i.e. you are XX) then you are female, whereas if you get an X and a Y (you are XY) then you are male. interestingly, pair 23 is the one pair of chromosomes where a gene on one (the X) may not have a match on the other (if it's Y). For example, the gene that determines colour-blindness is carried only on the X chromosome.
But we digress - this is supposed to be about bees!
There are two big differences in honey bees. Firstly, there are only 16 pairs of chromosomes. And secondly, only female bees get their chromosomes in pairs (i.e. a set from both parents for a total of 32). Male bees only have 16 unpaired chromosomes - all from their mother. Bee eggs are completely capable of developing into adult bees even if they are unfertilised - and they will always be male in this case. This process of being able to create children without fertilisation is known as parthenogenesis. And (male) bees produced through parthenogenesis have half as many chromosomes, so they are referred to as being "haploid". Female bees, with the full complement of 32 chromosomes, are "diploid".
Now, one of the consequences of this is that there is no Y chromosome. It's still the case that female bees are XX, but male bees only have one (of each) X chromosome - this is denoted as "Xo" (the "o" denoting "missing" or "absent").
So, one X makes a bee male, two XX makes her female, right? Well, this is what was thought until 2003, when researchers from the University of California found out it doesn't quite work like that. They found that sex determination isn't actually done by chromosome count - there's a specific gene that controls it. The gene is on the 3rd chromosome, and is called the "csd" or "complementary sex-determination" gene. Now, you might assume that this gene comes in two versions - male and female. But that would mean that a haploid (Xo) bee could have the "female" version in its one copy of chromosome 3 - in other words, a bee from an unfertilised egg could become female. But that never happens. So, what's actually going on?
It comes back to the alleles that we mentioned earlier. Remember the genes for eye colour in humans? These come in a number of different versions (blue, brown, green and others). Each different version of the gene is known as a different allele. And genes with multiple alleles are referred to as polymorphic - meaning that they come in different forms (poly=multiple, morphic=forms).
Now, the clue to how this works is in the name of the gene - "complementary sex-determination" gene. Why complementary? Simply, that different alleles of csd complement each other - in other words, they work together. When a bee has two different - complementary - versions of csd, she becomes female. If a bee has only one version of csd, then he will be male.
So, a quick recap - if a bee is Xo, it can only have one version of csd, so he must be male, and that's exactly what we observe. And if a bee is XX, and the two versions of csd are different (this is known as being heterozygous), then we get a female. There are around 20-25 different alleles of csd, so most of the time this is what happens.
But - hang on - it must be possible, even though unlikely, that sometimes an XX (diploid) bee, will have two identical copies of the csd gene? Indeed it is - in this case the gene is homozygous. But what happens then? Well, csd has a secondary effect - when two identical alleles are present, it changes the relative amounts of certain compounds in the skin of the larva when it hatches. This makes the larva smell different from the others, for around the first three days of its life. In fact, from a worker bee's perspective, it makes the larva smell delicious. So she eats it.
This means that adult bees with two identical csd alleles are never present in the hive. But if a csd-homozygous larva continues to be fed (and isn't eaten!) then it's possible for it to grow into an adult bee. But what does it become? Some scientists wanted to find out, so they hatched some csd-homozygous larvae in a laboratory, and fed them. After three days (when they stopped smelling like a tasty treat) they were returned to the hive where the workers continued to feed them. And then their cells were capped with wax (by the workers, as normal), the larvae underwent metamorphosis and later emerged as adult bees... which turned out to be...
Male! In other words, they are diploid (XX like female workers) but are actually drones. Having one version (but two copies) of the csd gene has the same effect as having only one copy - i.e. the bee is a male drone. But there are subtle differences. They are larger, heavier and have smaller testes. That last point is important - it means that the drones are, effectively, sterile. It is theoretically possible to inseminate a queen with diploid (XX) drone sperm to produced triploid (XXX - wowzers!) bees. But in practice it hasn't been achieved due the the extremely low sperm count of the diploid drones.
So there you have it - a haploid (Xo) bee will be a normal drone. A diploid (XX), csd-heterozygous bee will be a worker. And a diploid (XX), csd-homozygous bee will theoretically grow up to be a fat, sterile drone (but will actually be eaten by his sisters just after he hatches).
I'll leave you with one final fun fact. We've said that there are around 20-25 different alleles of the csd gene. Interestingly, a queen bee will mate with roughly 20-25 males before she starts laying. Co-incidence? I suspect not - it seems that bee mating behaviour has evolved to try to maximise the number of different csd genes, and therefore minimise or eliminate the production of diploid drones in the hive. Isn't that rather clever?
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